Vibrational efficacy

One issue that is particularly interesting for activated dissociation is the importance of translational vs. vibrational activation since this relates to the topology of the barrier location on the PES (see Section 2.3.1). In analyzing experiments, it has been traditional to define the vibrational efficacy rjv as in eq. (2.5). This analysis, however, assumes that A(v) is the same for all v and this may not be universally true. In this case, describing vibrational efficacy is more complicated. Very recently, experiments for CH4 dissociation on transition metals even combine supersonic nozzle molecular beams with laser state preparation techniques to probe the reactivity of specifically prepared vibration rotation states [115-118] (see Section 4.3.1.3). 

As Fig. 6 demonstrates, in the system H2/Cu the sticking probability is significantly enhanced if the impinging molecules are initially vibrationally excited. In order to quantify the effect the vibrational efficacy is introduced. It is defined as... 

The role of the initial vibrational state of the H2 molecule has been also analyzed. This was done by means of the so-called vibrational efficacy, which gives a measure of the effectiveness of the vibrational energy to promote the dissociative adsorption. The vibrational efficacy can be compufed using the simple formula ... 

Dfaz C, Olsen RA (2009) A note on the vibrational efficacy in molecule-surface reactions. J Phys Chem 130 094706... 

We have also learned that VMP is an effective tool in molecular spectroscopy and molecular dynamics studies. It is effective, in particular, for determination of IVR lifetimes and for studying the vibrational spectroscopy of states that are difficult to study applying other methods. The above-mentioned limit of the size of the molecule is irrelevant here. For observing the mode selectivity in VMP, the vibrational excitation has to survive IVR in order to retain the selectivity since the subsequent electronic excitation has to be from the excited vibrational state. In contrast, monitoring vibrational molecular dynamics relies only on the efficacy of the excitation of the specific rovibrational state. When IVR is fast and rovibrational distribution reaches equilibrium, the subsequent electronic excitation will still reflect the efficacy of the initial rovibrational excitation. In other words, whereas fast IVR precludes mode selectivity, it facilitates the unraveling of the vibrational molecular dynamics. 

Subsequently, Humbel, Sieber, and Morokuma (1996) generalized the IMOMM optuniza-tion scheme to the case where two different levels of QM theory were used instead of a QM/MM approach, and Svensson, Humbel, and Morokuma (1996) examined the relative efficacy of different combinations of levels for prototype problems. Corchado and Truhlar (1998) later proposed a refinement of that methodology to improve computed vibrational frequencies and Rickard et al. (2003) showed that a combination of MP2 and HF theories permits the calculation of high-quality NMR chemical shifts within the high-level system. 

A demonstration of the efficacy of MBER spectroscopy is the recent experiments on HF carried out by Bass, DeLeon, and Muenter [14]. In an effort to obtain Stark, Zeeman, and hyperfine properties, measurements were made that gave accurate values for both the ground and first excited vibrational levels of HF. Conventional resonance experiments can be done if the D = 1 state can be sufficiently populated. Using a color center IR laser to excite HF to u = 1, J = 1 levels, all the properties measured for the u = 0 and V = 1 states had essentially identical precision. The results included dipole moments, magnetic shielding anisotropies, rotational magnetic moments, magnetic susceptibilities, transition moments, and first and second derivatives with respect to internuclear separation of the properties. 

Given the subtle effects of structure on various calculated properties, it is desirable that inferences are made on the geometry-optimized stmctures of the clusters or complexes under investigation. This also facilitates the evaluation of the vibrational frequencies, because one can readily compare the calculated numbers with the experimentally observed frequencies or shifts. As a consequence, one can readily test the efficacy of the theoretical method employed in the calculations. 

Thermobalances are available in two different designs, i. e. a horizontal construction (Fig. 5-1) and vertical construction. For the vertical construction there are two different versions the top-loading balance, which has the oven above the balance (Fig. 5-2), and the thermobalance with the sample tray hanging on a thin hangdown wire into the oven below the balance (Fig. 2-4). The suppliers claim some advantages for the horizontal arrangement such as complete lack of buoyancy, the avoidance of condensation in the balance cabinet, and the reduction of sensitivity to vibration. However the last two points cannot be confirmed by the author s experience. Despite an efficacious gas flow, a diffusion of condensates was observed opposite to the flow direction of the gas. The sensitivity to vibrations seems to be comparable with the vertical design. Of the vertically constructed balances, the top loader is more convenient to manipulate. 

Koyama, K., Yoshida, A., Takeda, A., Morozumi, K., and Fujinami, T., 1996. Efficacy of methylcobalamin in subclinical uremic neuropathy as detected by measuring vibration perception thresholds. Nephrology. 2 25-28. 

Without any doubt, the most striking results of the dissociative adsorption measurements of CH4 on Nickel is the significant enhancement of reactivity for vibrationally excited molecules. For example, for CH4/Ni( 100), experiment [47,66] reveals that the vi vibrational state (see Fig. 2.18) has the largest efficacy ( jv) for promoting reaction. To analyze this observed behavior, and to shed some light on the physical mechanisms behind these observations, full-dimensional quantum simulations were performed [44,70]. To carry out these simulations the Reaction... 

A detailed analysis of the quantum results revealed the origin of this behavior. The increased efficacy of the v state arises from both mode softening and vibrationally non-adiabatic couplings. Furthermore this analysis revealed that most of the reactivity at the experimental surface temperature (475 K) is due to thermally assisted over-the-barrier processes, and not to tunneling. Tunneling becomes important at lower incidence energies and lower surface temperatures. 

Low-dimensional quantum dynamics studies of the dissociative adsorption of CH4 on Ni(l 11), as a function of the vibrational initial state, have also been carried out [52]. In this case, quantum dynamics simulations were performed using the multiconflguration time-dependent Hartree (MCTDH) method [1], Results obtained from this study are similar to those obtained for Ni(lOO) the efficacies of the stretching modes are larger than those of the bending modes, also in good agreement with experiments. 

Pathology is employed in biomedicine to identify and characterize the disease state of human tissue, using well-established optical microscopy techniques [79]. Often, disease-state determination involves the analysis of thinly sectioned, stained biopsied tissue in order to visualize various disease-specific pathologic markers. Although these examinations are typically made by highly trained practitioners, the potential exists to make the determinations more quantitative and less reliant on subjective observations by integrating the efficacy of vibrational spectroscopy with optical microscopy. This section describes... 

In summary there is good and increasing evidenee for the efficacy of vibrational spectroscopy techniques in cancer screening and diagnosis. The next phase will be validation of these techniques in carefully designed studies of sufficient statistical power to prove efficacy in clinical practice. 

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